The Pillow Lavas of Sakhalin and the Kurile Islands and Their Significance for the Solution of the Spilite Problems

Abstract

The paper contains data on age-distribution of various pillow lavas of the Sakhalin and the Kurile Islands and on the peculiarities of their petrographic and chemical compositions. The presence of marine fossils within the rocks underlying the pillow lavas and the peculiar structure of these volcanic rocks testify to their undersea origin. The Sakhalin pillow lavas are subdivided into five groups: Jurassic-Early Cretaceous, Late Cretaceous, Early Miocene, Middle Miocene and Late Miocene-Pliocene. The same formations of the Kurile Islands are subdivided into three groups: Late Cretaceous, Early Miocene and Pliocene. The correlation of the petrographic and chemical compositions of the pillow lavas of different ages confirms the viewpoint of those students who state that the peculiarities of mineralogical and chemical compositions of the spilites are not caused by the occurrence of independent spilitic magmas, but are the consequence of the transformation of common volcanic rocks under the conditions peculiar to folded geosynclinal areas.